Epoxy resin has been used in copper clad laminates and printed circuit boards for many years, the main reason thereof is that the adhesion strengths between epoxy resin and reinforcing materials such as glass fiber cloths, glass fiber mats and paper etc. are good, no volatile component is emitted during curing, and shrinkage is less during molding; the resulted copper clad laminate possesses superior mechanical strength, electric insulation, chemical resistance, good dimension accuracy and easy to be processed, thus it becomes a most important raw material for printed circuit boards.
At the moment, the copper clad laminate (CCL) used in printed circuit boards is mainly FR-4 based on not only quantity but also technical level, but the development of the electronics industry is advanced rapidly by leaps and bounds, the important related components—printed circuit boards should also keep up with the pace of time.
As for system products, light, thin, short, small, power saving and durable are the trend, nevertheless the size of the corresponding electronic components becomes smaller at continuously elevated operating frequency, decreased voltage, reduced transistor power consumption and less tolerate voltage noise, thus it is resulted the emerging one by one of the problems which are originally are not necessary to be considered in the low-frequency area; only in terms of printed circuit boards of the interconnection industry, two major development trends has already been generated; firstly the high density printed circuit board: the main technologies are fine circuits, small holes, blind holes, buried holes; secondly high-frequency electronic component carrier substrates and printed circuit boards for high-speed electronics: the main technologies include low dielectric constant, low dissipation factor for board materials and thin medium layer materials and the precision impedance control, etc.
21st century will become a video generation, the high-frequency high-speed application is one important trend of development of the future high-speed printed circuit board (PCB), the traditional FR-4 substrate can still meet the most current printed circuit board industry demand, and holds the largest market share; however, with increasing demand in the material properties and cost considerations, the standard FR-4 substrate can meet the demand of generic products, but as for the high frequency transmission products, the substrate materials are requested to have higher qualities, thus the low dielectric constant, low dissipation factor substrate just complies with the information products to meet the requirements of high-speed and high-frequency and coordinates the communication products for the massive and rapid transmission of voice and video data.
The copper clad laminate (CCL) material is mainly formed by a reinforcing material and a resin composition, the outer layer thereof is pasted together with copper foils, so the resin composition will be one of the main factors to impact electric properties of the substrate. The present patent describes the development of the resin composition to achieve the effectiveness of improving electric properties of substrate boards.
In patent BE-627887, it is mentioned that the copolymer of maleic anhydride and styrene is used as the curing agent of the epoxy resin, but the disadvantages of this epoxy resin composition are low glass transition temperature (Tg) and poor heat resistance so that it is not suitable for the application of copper clad laminates (CCL) and printed circuit boards (PCB) manufacturing.
When anhydride-type curing agent (hardener) is used with the epoxy resin, it will react rapidly at room temperature upon the addition of an accelerator (promoter), thus this is not suitable to be used in the field of printed circuit boards.
The resin system currently used for copper clad laminates and printed circuit boards is epoxy resin, and generally the standard FR4 substrate is used, whose main ingredient is bisphenol-A epoxy resin or brominated epoxy resin manufactured from tetrabromobisphenol-A wherein the curing agent is dicyandiamide, besides an accelerator and solvents are added; the disadvantages of the epoxy resin composition are a low glass transition temperature (Tg) (120-140) and poor heat resistance, if the multi-functional epoxy resin is used to replace bisphenol-A epoxy resin to elevate crosslinking density and thereby eliminate the disadvantage of the low glass transition temperature (Tg), but it is without much contribution to improve the heat resistance and electrical properties.
U.S. Pat. No. 6,509,414 reveals the use of styrene-maleic anhydride copolymer (SMA) as a resin curing agent, which can improve the heat resistance of a general difunctional epoxy resin; besides, a co-crosslinking agent is used, for example, styrene-maleic anhydride copolymer (SMA) is used with co-crosslinking agent, such as tetrabromobisphenol-A, tetrabromo-bisphenol-A diglycidyl ether (TBBADGE), to improve the glass transition temperature (Tg) of base materials; wherein the equivalent proportion of acid anhydride, aromatic hydroxy group(OH) and epoxy resin is 50%˜150% in the mixed resin. Revealed by the examples, it is clearly understood that if the equivalent proportion is increased from 70% to 110%, then the DSC glass transition temperature (Tg) is elevated from 122 to 155, but if the equivalent proportion is further increased from 110% to 150%, the DSC glass transition temperature (Tg) drops to 137 from 155. This phenomenon is advised that when the equivalent proportion is more than around 110%, the crosslinking agent will no longer be able to enhance the crosslinking density, so that the DSC glass transition temperature (Tg) cannot be raised.
Nowadays copper clad laminate (CCL) and printed circuit boards (PCB) manufacturing trends from the halogen system (mainly brominated flame retardant agent TBBA) towards a non-brominated (mainly phosphorus based flame retardant agent) or even a halogen-free system; the modified maleic anhydride copolymer curing agent synthesis of the present invention is in response to the future environmental protection demand, the present system may be a halogen system, a phosphorus system or a halogen-free system.